A standard for a wireless local area network (WLAN) technology has been developed as IEEE (Institute of Electrical and Electronics Engineers) 802.11 standard. IEEE 802.11a or IEEE 802.11b uses an unlicensed band in 2.4 GHz or 5 GHz, IEEE 802.11b provides transmission speed of 11 Mbps and IEEE 802.11a provides transmission speed of 54 Mbps. IEEE 802.11g provides transmission speed of 54 Mbps in a manner of applying Orthogonal Frequency Division Multiplexing (OFDM) in 2.4 GHz. IEEE 802.11n provides transmission speed of 300 Mbps for 4 spatial streams in a manner of applying Multiple Input Multiple Output-OFDM (MIMO-OFDM). IEEE802.11n supports a channel bandwidth up to 40 MHz. In this case, IEEE802.11n provides transmission speed of 600 Mbps.
IEEE 802.11af standard is a standard set to regulate an operation of an unlicensed device in a TV whitespace (TVWS) band.
The TVWS is a frequency assigned to a broadcast TV and includes an Ultra High Frequency (UHF) band and a Very High Frequency (VHF). The TVWS means a frequency band permitted to an unlicensed device to use under a condition that the unlicensed device does not impede a communication of a licensed device operating in a corresponding frequency band. The licensed device can include a TV, a wireless microphone, and the like. The licensed device can be called an incumbent user or a primary user. And, in order to solve a coexistence problem between unlicensed devices using the TVWS, it may be necessary to have such a signaling protocol as a common beacon frame and the like, frequency sensing mechanism, and the like.
Although operations of all unlicensed devices are permitted on 512˜608 MHz and 614˜698 MHz except several special cases, a communication between fixed devices is only permitted on 54˜60 MHz, 76˜88 MHz, 174˜216 MHz, 470˜512 MHz. A fixed device indicates a device performing a signal transmission at a fixed position only. IEEE 802.11 TVWS terminal means an unlicensed device operating by using IEEE 802.11 MAC (media access control) and a physical layer (PHY) in a TVWS spectrum.
The unlicensed device wishing to use the TVWS should provide a protection function for a licensed device. Hence, the unlicensed device should check whether the licensed device occupies a corresponding band before starting a signal transmission in the TVWS.
To this end, the unlicensed can check whether the corresponding band is used by the licensed device in a manner of performing a spectrum sensing. A spectrum sensing mechanism includes an energy detection scheme, a feature detection scheme, and the like. If strength of a signal received from a specific channel is greater than a certain value or a DTV preamble is detected, the unlicensed device can judge that the specific channel is currently used by the licensed device. And, if it is judged that the licensed device currently uses a channel adjacent to the channel currently used, the unlicensed device should lower a transmit power.
And, the unlicensed device should obtain channel list information capable of being used by the unlicensed device in a corresponding area in a manner of accessing a database (DB) via the internet or a dedicated network. The DB is a database storing and managing information on the licensed device registered in the DB and a channel use information, which dynamically varies according to a geographical location of the corresponding licensed devices and hours of use.
In explaining the present specification, a white space band includes the aforementioned TVWS, by which the present invention may be non-limited. In the present specification, a terminology of white space band means a band preferentially permitting an operation of the licensed device and the band permitting an operation of the unlicensed device only when a protection for the licensed device is provided. And, a white space device means a device operating in the white space band. For instance, a device according to an IEEE 802.11 system may become an example of the white space device. In this case, the white space device may indicate the unlicensed device operating in the white space band using the IEEE 802.11 MAC (Medium Access Control) layer and the PHY (Physical) layer. In particular, a general AP according to 802.11 standard and/or an STA operating in the white space band may correspond to an example of the unlicensed device.